Large effects of tiny structural changes on the AIE-TADF type xanthone derivatives in mechano-responsive luminescence and electroluminescence

In this work, two compounds with aggregation-induced emission (AIE) and thermally activated delayed fluorescence (TADF) properties (XT-T and XT-OT) which have the xanthone moiety as an electron withdrawing group were synthesized and studied. Both molecules exhibited the mechano-responsive luminescence (MRL) effect, in which a crystal of XT-OT could exhibit a bathochromic shift of 101 nm to achieve a wide-range emission transition from blue to yellow after grinding, compared to 34 nm for crystal XT-T. Such a high color-difference in the maximum emission peak was rarely reported in MRL materials. Analysis of crystal structures showed that small differences in structure could give rise to variable conformations and packing patterns in different aggregated states. The application of two compounds as light-emitting layers in organic light-emitting diodes (OLEDs) revealed the impact on device performance by their structural difference. The results presented here could provide a complementary strategy to design new multi-function materials.